Method of making solid fertilizers.



y ukm "B. P. HALVO'RSEN. METHOD or MAKING SOLID FERTILIZERS.APPLIOAI'ION IIIJEDAPB. 25, #1908.

936 31 7 Patented Oct. 12, 1909.

Witnesses. Inventor.

NITED STATES PATENT OFFICE. v

BIRG-ER FJELD HALVORSEN, OF CHRISTIANIA, NORWAY, ASSIGNOR T0 NORSKHYDRO- ELEKTRISK KVAELSTOFAKTIESELSKAB, OF CHRISTIANIA, NORWAY.

Specification ofl etters Patent.

METHOD OF MAKING SOLID FERTILIZERS.

.Patented Oct. 12, 1909.

Application filed April 25, 1908. Serial No. 429,206.

Solid Fertilizer; and I .do hereby declare the following to be a full,clear, and exact description of the invention, such as will enableothers skilled in the art to which it appertains to make and use thesame. I

My invention relates to a method of manufacturing a solid fertilizercontaining nitrogen and phosphoric acid.

In the modern manufacture of nitric acidfrom atmospheric air there isobtained as a primary product a cheap, but rather dilute nitric acid. Itis advantageous to utilize this dilute nitric acid as a solvent forphosphates, instead of sulfuric acid, which is at present generallyemployed for this purpose. The advantages which may. be 'obtained bysuch a procedure are obvious, the sulfuric acid adding to the fertilizeronly a valueless component, while the nitric acid supplies to itadditional plant food, namely,

nitrogen.

'The process at the first glance appears to be very simple. Thephosphate (for instance a poor or valueless apatite) is dissolved-in anequivalent quantity of the acid,

thereby obtaining a solution of mono-calcium-phosphate and calciumnitrate. The difliculty lies in transforming the substance into a solid.By adding lime or calcium carbonate the so-called di-phosphate may, ofcourse, be precipitated, leaving a remainder of pure calcium nitrate;this would, however, impair the value of the product in the first place,(as di-calcium-phosphate is of less value than mono-calcium-phosphate,)and, further, entails expenses for lime, filtering operations, (whichare very difficult,) and for evaporation.

It is diflicult to elfect a direct evaporation of the solution, first,because it is difficult to procure a suitable material for theevaporation pans, that is to say, a material capable of resisting theaction of the acid liquor, and, secondly, because loss of nitric acidand reversion of the phosphoric acid are liable to arise, because thephosphoric acid expels nitric acid when heated. The latter difficulty,however, may be remedied to acertain extent, if not entirely avoided, by

effecting the evaporation at a low temperature, for instance in vacuum.

My invention has for its object to avoid all the difiiculties mentionedabove, and to produce a valuable solid substance in which phosphoricacid is present in its most advantageous condition, namely, as amonocalcium-phosphate entirely soluble in water, a suitable apparatusfor carrying out my process being shown in the accompanying drawing invertical section.

The process is suitably carried out in the following manner: The dilute,40% nitric acid produced from atmospheric air is employed for dissolvingan equivalent quantity of tri-calcium-phosphate according to thefollowing equation;

The solution is suitably etl'ected in irrigation towers filled withphosphate, for eX- ample as shown in the; accompanying drawing, or inlixiviating vessels, as may be preferred. In both cases the principle ofcounter-current is applied, and heating is preferably provided for bymeans of hot gases from electric furnaces in which oxids of nitrogen arebeing produced.

In the apparatus illustrated in the draw- .ing the hot gases enter theirrigating tower I through pipe 2 at the bottom and escape through pipe3 at the top of the tower. The acid is supplied by means of thesprinkler pipe 4;, passes over the phosphate rock, which is in thetower, and is collected in the basin 5 at the base of the tower. To theacid solution obtained, in one way or another, is added' a quantity ofcalcined calcium nitrate still warm from the calcination, andcorresponding to the quantity of water in the acid solution. Some of theWater is thereby evaporated, and the remaining quantity is boundchemically by the calcium nitrate as water of crystallization. So muchcalcium nitrate-is added, that there is, in total, 31-1.,(1 to eachmolecule of Ca(NO Owing to the evaporation, a product is obtainedcontaining at least 15% P 0 and 11% N; and on being cooled the entireproduct coagulates to a solid, hard mass, which can be crushed into apowder.

' The calcination of the nitrate of lime is suitably efiected by heatingit directly with ion - rotating drums. The quantity of gas to be passedthrough the drum. is successively made greater in order that thetemperature may be kept below the smelting-temperature of the nitrate.The smelting point is the higher the more water is evaporated. Thetemperaturemust never go over 300 C., in order to avoid destruction ofthe nitrate. The successive raisin of the temperature may easily becontrol ed by the quantity of gas, vlvhich is let in through a throttlevalve. c a1m 1. Method of manufacturing a solid fer- I tilizer,containing nitrogen and phosphoric acid, which comprises dissolvingphosphates in dilute nitric acid and adding calcined calcium nitrate tothe resulting solution in such a quantity as to unite with the excess ofwai ter present as Water of crystallization.

y 2. Method of manufacturing a solid fer- 20 'tilizer containingnitrogen and phosphoric acid, which comprises d solving phosphates innitric acid, and adding hot' calcined oal- BIRGE R FJELD HALVORSEN.

Witnesses:

HENRY BORDEWIOH, MICHAEL ALGER.

